1. Field of the Invention
The present invention relates to sensing the loss of a signal ground, in an electronic system including both signal and power grounds, and the coupling of signal ground to power ground responsive thereto.
2. Description of the Prior Art
In automotive and military applications, it is common to have both power and signal grounds in order to isolate significant switching transients in the power system from interfering with the small voltages normally present on the digital signal circuits. For example, different wiring paths and circuits, including ground returns, are used for systems having relatively large power requirements, such as starter motors, power windows and air conditioning systems, as compared to systems employing small signal sensors, controllers and minor transducers, such as fuel level sensors, temperature sensors, engine control electronics, etc.
However, when two different ground returns are provided, it is possible in harsh environments, such as automotive systems, that either the signal or the power grounds can be lost due to a broken wire, a loose connector or a corroded interconnect. When one ground is lost or becomes intermittent, ground loops and bias offset voltages may be induced in sensor and small signal controllers which disrupt the operation or reduce the accuracy of these important systems.
The present invention senses the loss of the signal ground and then substitutes the power ground for the signal ground until the power is reset or, if the problem persists, until the source of the problem can be corrected. Since the battery voltage can drop to as low as 5.5 volts during cold cranking conditions and can be as high as 24 volts during jump starting conditions, the circuitry for controlling the ground system switching must be capable of operating over the entire range of 5.5 to 24 volts.
It is therefore an object of the present invention to sense any interruption in the signal ground used by the power and electronics systems of an automotive vehicle, and to switch and to latch the signal ground to the power ground when the signal ground is interrupted.